1. Field of the Invention
The present invention relates to a positive electrode for a lithium-sulfur battery and a lithium-sulfur battery and article of manufacture including the same, and more particularly, to a positive electrode for a lithium-sulfur battery providing a lithium-sulfur battery with a high capacity.
2. Description of the Related Art
The recent trend toward more compact and lighter portable electronic equipment has increased a need for a high performance and high capacity battery to provide electric power for portable electronic equipment. The low equivalent weight of lithium renders lithium attractive as a battery electrode component for improving weight ratios. The low equivalent weight and low cost, as well as the nontoxicity of sulfur, also renders sulfur an attractive candidate for a battery component.
A lithium-sulfur secondary battery uses a sulfur-based compound with sulfur-sulfur bonds as a positive active material, and lithium metal or a carbon-based compound as a negative active material. The carbon-based compound in which intercalation chemistry occurs, includes graphite, graphite intercalation compounds, carbonaceous materials, and carbonaceous materials inserted with lithium. Upon discharge (electrochemical reduction), sulfur-sulfur bond breaking occurs, resulting in a decrease in the oxidation number of S, and upon recharging (electrochemical oxidation), a sulfur-sulfur bond formation occurs, leading to an increase in the oxidation number of S.
However, employing a positive electrode based on elemental sulfur in an alkali metal-sulfur battery system has been considered problematic. Although theoretically the reduction of sulfur to an alkali metal-sulfide confers a large specific energy, sulfur is known to be an excellent insulator, and problems using sulfur as an electrode have been noted. Common problems referred to by those skilled in the art include very low percentages of utilization and a low lifecycle characteristic as a result of the sulfur and lithium sulfide (Li2S) dissolved and diffused from the positive electrode.
One scheme to address such problems is the choice of a binder. The requirements for the binder include: an ability to enhance the mechanical integrity of the positive electrode, no reaction with an electrolyte, stability at battery working temperatures, solubility in organic solvents used in slurry, and insolubility in electrolytes.
Examples of conventional binders that satisfy these requirements are polyethylene oxide or polyvinyl pyrrolidone. However, polyethylene oxide has poor adhesion, and polyvinyl pyrrolidone has somewhat poor adhesion. Such poor adhesion necessitates the use of a large amount of binder, which results in a decrease in the amount of positive active material in the positive electrode, causing a decreased capacity.